One method used to lower overall NOX emissions in a gas turbine engine is to minimize the reaction zone temperature below the level at which NOX emissions are formed. For example, commonly owned U.S. Pat. No. 6,868,676 to Haynes, entitled “Turbine Containment System and Injector Therefore”, shows the use of a secondary combustion system downstream of the primary combustion system. This secondary combustion system includes a number of injectors to inject fuel and other fluids at the head end of the combustor. The fuel burns quickly due to the high temperature environment and relieves the temperature of combustor head end so as to lower overall NOX emissions. U.S. Pat. No. 6,868,676 is incorporated herein by reference.
Although testing of this secondary combustion system has shown promise in reducing overall NOX emissions, such a system has not been widely adopted because of a concern with the durability of the fuel injectors. Specifically, the fuel injectors are positioned within the hot gas pathway. Any loss of cooling to the injectors therefore may result in the failure of the injectors and possible damage to the turbine as a whole.
There is a desire therefore for an improved secondary combustion system. Such a system should promote lower NOX emissions while also being durable and reliable.